The present invention relates to a thin film magnetic head which is mounted on a magnetic disk unit for use in recording and reproducing information, and more particularly to a compound type thin film magnetic head having an element of magnetoresistance effect (MR thin film magnetic head).
A conventional compound type thin film magnetic head comprises a substrate made of a non-magnetic material, a lower shield layer of a magnetic material formed on the substrate, a first non-magnetic layer formed on the lower shield layer, a common magnetic pole of a magnetic material formed on the first non-magnetic layer, a second non-magnetic layer formed on the common magnetic pole, a conductive coil formed on the second non-magnetic layer through a first insulation layer, a second insulation layer overlaid on the conductive coil, and an upper magnetic pole of a magnetic material formed on the second insulation layer. A front end of the upper magnetic pole is directly kept in contact with the first non-magnetic layer while a rear end of the upper magnetic pole is directly kept in contact with the common magnetic pole. Accordingly, a yoke structure is formed by the upper magnetic pole and the common magnetic pole. The conventional compound type thin film magnetic head further comprises an element of magnetoresistance effect in a front end of the first non-magnetic layer. The common magnetic pole is operable as both an upper shield layer and a lower magnetic pole. The element of magnetoresistance effect is therefore magnetically isolated with the lower shield layer and the common magnetic pole by the first non-magnetic layer. On the other hand, the conductive coil is therefore electrically isolated with the common magnetic pole and the upper magnetic pole by the first insulation layer and the second insulation layer.
In a recent hard disk drive, an NLTS compensation circuit has been used for compensating a non-linear bit shift (NLTS) and thereby reducing mutual interference between adjacent bits in order to achieve a large recording density. However, it comes to the limits inevitably that the non-linear bit shift (NLTS) is compensated by the NLTS compensation circuit.
On the other hand, an increase or a decrease of the above-mentioned non-linear bit shift (NLTS) depends upon an inductance of a recording portion in an MR thin film magnetic head. In the conventional compound type thin film magnetic head, the common magnetic pole has a considerably wide area, compared with the upper magnetic pole. As a result, the inductance of a recording portion therein has a large value, so that the non-linear bit shift (NLTS) inevitably becomes large. Accordingly, the conventional compound type thin film magnetic head has already reached a region exceeding the aforesaid limits to which the non-linear bit shift (NLTS) is compensated by the NLTS compensation circuit. This causes a problem that a recording density of a hard disk drive is prevented from being improved.